怎样判断一个类型是"操作简单"类型？即持有单个值 [英] How do I tell if a type is a "simple" type? i.e. holds a single value

问题描述

typeof(string).IsPrimitive == false
typeof(int).IsPrimitive == true
typeof(MyClass).IsClass == true
typeof(string).IsClass == true
typeof(string).IsByRef == false
typeof(MyClass).IsByRef == true // correction: should be false (see comments below)

我有一个实例T的新实例，如果它是一个复杂类，填充的方法其从一组源数据值的属性。

I have a method that instantiates a new instance of T and, if it's a "complex" class, fills its properties from a set of source data values.

（一）如果T是一个简单的类型（如字符串或int或其他类似的），从快速转换源数据，以T为被执行。

(a) If T is a simple type (e.g. a string or an int or anything else similar), a quick conversion from the source data to T is to be performed.

（二）如果T是一个类（而不是一些简单的像字符串），那么我会使用Activator.CreateInstance和做一点反思来填充字段。

(b) If T is a class (but not something simple like string), then I'll use Activator.CreateInstance and do a bit of reflection to populate the fields.

是否有一个快速和简单的方式告诉我是否应该使用方法（a）或（b）法？这个逻辑将和T泛型方法的类型参数内部使用。

Is there a quick and simple way to tell if I should use method (a) or method (b)? This logic will be used inside a generic method with T as the type argument.

推荐答案

字符串可能是一个特例。

String is probably a special case.

我想我会做.....

I think I would do.....

bool IsSimple(Type type)
{
    return type.IsPrimitive 
      || type.Equals(typeof(string)));
}

---

修改：

有时候，你需要支付一些情况下，如枚举和小数。枚举是一种特殊的在C＃中的类型。小数像任何其他结构。与结构的问题是，它们可能是复杂的，它们可以是用户定义的类型，它们可以只是一个数字。所以，你没有任何其他的机会比知道它们加以区分。

Sometimes you need to cover some more cases, like enums and decimals. Enums are a special kind of type in C#. Decimals are structs like any other. The problem with the structs is that they may be complex, they may be user defined types, they may be just a number. So you don't have any other chance than knowing them to differentiate.

bool IsSimple(Type type)
{
  return type.IsPrimitive 
    || type.IsEnum
    || type.Equals(typeof(string))
    || type.Equals(typeof(decimal));
}

处理可空的同行也有点棘手。可空本身是一个结构。

Handling nullable counterparts are also a bit tricky. The nullable itself is a struct.

bool IsSimple(Type type)
{
  if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>))
  {
    // nullable type, check if the nested type is simple.
    return IsSimple(type.GetGenericArguments()[0]);
  }
  return type.IsPrimitive 
    || type.IsEnum
    || type.Equals(typeof(string))
    || type.Equals(typeof(decimal));
}

测试：

Test:

Assert.IsTrue(IsSimple(typeof(string));
Assert.IsTrue(IsSimple(typeof(int));
Assert.IsTrue(IsSimple(typeof(decimal));
Assert.IsTrue(IsSimple(typeof(float));
Assert.IsTrue(IsSimple(typeof(StringComparison));  // enum
Assert.IsTrue(IsSimple(typeof(int?));
Assert.IsTrue(IsSimple(typeof(decimal?));
Assert.IsTrue(IsSimple(typeof(StringComparison?));
Assert.IsFalse(IsSimple(typeof(object));
Assert.IsFalse(IsSimple(typeof(Point));  // struct
Assert.IsFalse(IsSimple(typeof(Point?));
Assert.IsFalse(IsSimple(typeof(StringBuilder)); // reference type

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